The separation of various substances through selective absorption using a simulated moving bed of adsorbent is an example of a process in which a multiport rotary disc valve is useful. Simulation of a moving sorbent bed is described in U.S. Pat. No. 2,985,589 (Broughton et al.), which is mentioned above. In accomplishing this simulation, it is necessary to connect a feed stream to a series of beds in sequence, first to bed no. 1, then to bed no. 2, and so forth for numerous beds, the number of beds often being between 12 and 24. These beds may be considered to be portions of a single large bed whose movement is simulated. Each time the feed stream destination is changed, it is also necessary to change the destinations (or origins) of at least three other streams, which may be streams entering the beds, such as the feed stream, or leaving the beds. The moving bed simulation may be imply described as dividing the bed into series of fixed beds and moving the points of introducing and withdrawing liquid streams past the series of fixed beds instead of moving the beds past the introduction and withdrawal points. A rotary valve used in the Broughton process may be described as accomplishing the simultaneous interconnection of two separate groups of conduits.
There are many different process requirements in moving bed simulation processes, resulting in different flow schemes and thus variations in rotary valve arrangement. For example, in addition to the four basic streams described in Broughton (U.S. Pat. No. 2,985,589), it may be desirable to utilize one or more streams to purge, or flush, a pipeline or pipelines. A flush stream is used to prevent undesirable mixing of components. The flush substance is chosen to be one which is not undesirable for mixing with either main stream, that being purged or that which enters the pipeline after flushing is completed. U.S. Pat. No. 3,201,491 (Stine et al.) may be consulted for information on flushing lines as applied to the process of Broughton (U.S. Pat. No. 2,985,589). It may be desirable to pass fluid through a bed or beds in the reverse direction from normal flow. This is commonly known as backflushing, a subject treated in U.S. Pat. No. 4,319,929 (Fickel). Other applications for various arrangements of multiport rotary disc valves may be seen in U.S. Pat. Nos. 4,313,015 (Broughton); 4,157,267 (Odawara et al.); 4,182,633 (Ishikawa et al.); and 4,409,033 (LeRoy).
Multiport rotary disc valves of the general arrangement shown in the above patents have been fabricated in various sizes up to valves utilizing 4½ foot diameter rotors. These valves have seven concentric circumferential grooves, or tracks, and 24 ports spaced around the periphery of the stator. A single valve of this size weighs approximately 26,000 pounds, has an overall height of about 15 feet, and occupies a plan area of approximately 8½ by 8½ feet. These figures do not include a separate hydraulic power unit used with the hydraulically driven actuator mounted on the valve proper.
U.S. Pat. No. 4,764,276 (Berry et al.) discloses a continuous contacting device wherein a fluid stream may be contacted with a particulate exchange material. The device includes a plurality of rotating chambers filled with particulate material. Fluid is supplied individually to these chambers through a plurality of feed ports which are in periodic fluid communicating relation with each of the rotating adsorbent chambers.
Large rotating turntables or carriages supporting sorbent chambers filled with adsorbent material and liquid present an engineering problem to uniformly support the weight and the movement of the rotating sorbent chambers, and represent a technical challenge to maintain the stator and rotor seating surfaces in proper registration and in fluid-tight contact to prevent loss of fluid or contamination of the final product.
Rotary valves typically comprise a discoid stator which is in a fixed position and a rotor which is indexed through a predetermined cycle to direct the distribution flows in a simulated moving bed process. As mentioned hereinabove, commercial use of rotary valves in high capacity processes has generally employed rotary valves having large diameter lower stators having concentric groves or pipes and supporting an upper rotor for directing the flows in continuous contacting devices for carrying out simulated moving bed processes. Such valves are employed in conjunction with a single multi-stage sorbent chamber having multiple inlets and outlets to create the necessary concentration profiles throughout the single adsorbent chamber. Small-scale processes have employed upper fixed position stators having a plurality of sorbent chambers which are supported in direct fluid communication with a lower rotor, wherein the rotor and all of the adsorbent chambers are on a turntable structure which rotates about the stator with the indexing of the valve rotor. Such turntable arrangements also suffer from the requirement for very large plot areas, and the engineering and technical difficulties of maintaining a proper seal during the rotation or indexing of the valve through the cycle. The turntable structure requires the uniform and symmetrical arrangement of the adsorbent chambers disposed about the center of rotation of the turntable. It can be appreciated that it is desirable to use an apparatus of less bulk and weight to accomplish the same functions and avoid rotary valves with large plot area footprints, and avoid the technical and engineering problems related to maintaining a fluid-tight seal while rotating all of the adsorbent chambers with the rotation of the rotor.